To improve fuel economy, hybrid electric vehicles (HEVs) may utilize regenerative (regen) braking, in which kinetic energy is converted by an electric machine into storable energy during braking and then made available for vehicle propulsion. Currently, parallel regen braking is controlled via a BOO (Brake On/Off) switch. When the BOO switch closes during a braking event, the regen powertrain applies a fixed magnitude of brake torque to stop the vehicle. Although the torque can be ramped up and down via cal parameters, torque control is limited due to the step function behavior of the BOO switch. As a result, vehicle braking events can be somewhat uneven.
The parallel regeneration brake system may include a regeneration brake system pedal travel sensor which senses the travel position of the vehicle brake pedal over a continuous range of positions of the pedal. Therefore, signals from the sensor may be used to control operation of the BOO switch such that the BOO switch controls the brake torque of the regen powertrain over a continuous range, evening out the vehicle braking events.
Accordingly, a parallel regeneration brake torque modulation system and method in which a regeneration brake system pedal travel sensor is used to control parallel regenerative braking in a vehicle are needed.